Sleep in birds and mammals appears to be a homologous phenomenon but the question arises as to whether it evolved separately in the two groups or evolved first in their common ancestors, the reptiles. Previous studies have failed to demonstrate conclusively that behavioral sleep in reptiles is the same phenomenon physiologically speaking. We believe that we have established that under proper conditions, particularly with regard to temperature, there is slow wave sleep in the crocodilians, the group with the closest relationship to birds, phylogenetically speaking. We are attempting by anatomical studies to establish the anatomical control system for sleep in crocodilians and to demonstrate whether or not it is the same system seen in birds and mammals. As yet there is only one reference in the literature which indicates that active sleep exists for crocodilians. We are seeking to establish or rule out active sleep as a reptilian characteristic. We believe that thinking of eye movement (REM) as the main facet of active sleep investigators are deflected from other important manifestations of this state.